One should not offer salah behind such staunch ghair muqallid who counts all the Muqallids as mushrik, and abuses Hadhrat Imam Abu Hanifa (رحمة الله) as well as has false beliefs. Such person is fasiq (transgressor) without any doubt and one is forbidden in the Hadith to offer salah behind a fasiq person.
ولا يؤم فاجر مؤمناً (ابن ماجہ).
Allah knows Best!
Darul Uloom Deoband